This revised application is a request for competitive renewal of a prospective, longitudinal study of the emergence of autism in infant siblings of children with autism (AU sibs) and low risk controls (tested at 6 months, 14, 24 and 36 months). Data from the existing R01 show that autism is present by 14 months, with the phenotype being characterized by deficits in social, communication, and repetitive and stereotyped patterns of behavior and interest. Symptoms become more severe in about over a third of the toddlers with ASD. In the renewal, there will be four groups of participants: (1) younger siblings of children with autism;(2) low-risk controls;(3) verbal probands through whom the younger siblings were ascertained;and (4) children with Specific Language Impairment (SLI) who will have the exact same assessment protocol at the same ages as groups 1-3 (Dr. Mabel Rice's sample from University of Kansas). The specific aims of the proposed continuation are to follow these children until they are 6 to 8 years of age in order to: (1) examine early school-age 'outcomes'of children who manifested autism spectrum disorder (ASD), language impairment, or no impairment during toddlerhood;(2) identify 14-month-old predictors of school-age ASD and the broader autism phenotype (BAP);and (3) determine whether the language impairment associated with the BAP and ASD overlap with, and are distinguished from, SLI in predicted ways between 4 and 8 years of age. Likewise, whether autism-related social deficits are associated with SLI will be examined. Assessments will measure IQ, adaptive functioning, language (phonological, morphosyntactic, vocabulary, pragmatics), reading, social, developmental psychopathology, and autism symptoms. There is complete overlap of data for the all sites. Data will be collected at yearly intervals. Analyses will involve the use of regression models, and growth curve analysis. This will be the first study of its kind to follow children at high risk for autism and related disorders from infancy to school age, and the first to prospectively and longitudinally compare linguistic functioning in autism, the BAP, and SLI.